Determining top-dead-center (tdc) of reciprocating compressor

ABSTRACT

Various embodiments include approaches for determining a top-dead-center (TDC) of a reciprocating compressor. In some cases, an apparatus includes: a pressure transducer configured to measure pressure fluctuations inside a compressor cylinder and convert the pressure fluctuations into an asynchronous waveform; and at least one computing device operably connected with the pressure transducer, the at least one computing device configured to: extract a data set representing piston angles over a single revolution of a piston within the compressor cylinder from the asynchronous waveform; remove data representing invalid piston angles from the data set to form a refined data set; determine an average piston angle for the single revolution from the refined data set; and adjust the refined data set to identify a top-dead-center (TDC) position of the piston within the compressor cylinder.

FIELD OF THE INVENTION

The subject matter disclosed herein relates to compressor systems. Moreparticularly, the subject matter relates to diagnostics of compressorsystems.

BACKGROUND OF THE INVENTION

A vast majority of diagnostics for reciprocating compressors requiredata about the mechanical top-dead-center (TDC) position of thecompressing piston inside the compressor's cylinder. Other data aboutthe reciprocating compressor is indexed to the TDC position data.Conventional diagnostic approaches for determining this TDC position ona reciprocating compressor require that the compressor be powered off(shutdown). With the compressor shut down, a dial indicator or level maybe used to determine the TDC position. With the TDC established, aproximity probe may be installed to view an event on the crankshaft orcrosshead. The structure(s) viewed by the proximity probe may bedetectable on a once-per-turn or multiple-event-per-turn basis, or acombination thereof. After determining the TDC position and installingthe proximity probe, the compressor maybe re-started. The conventionalapproach relies upon this proximity probe and an event (referred to as aphase-reference transducer) along with requisite wiring connecting theprobe and the transducer, to mark TDC for each revolution. Modificationof the compressor and/or crankshaft, installation of wiring, andverification of components add expense to the diagnostic system.

Additionally, in conventional approaches, the event data must becollected simultaneously across the pressure transducer and thephase-reference transducer so that the TDC marked by the phase-referencetransducer can be accurately related to the pressure transducer. Theneed for this type of simultaneous data collection nearly excludeswireless transmission of data from the compressor as it can be difficultto ensure simultaneous transmission of data from various points,particularly in industrial environments.

Prior example approaches for determining the TDC of a reciprocatingengine include comparing measured event data to a thermodynamic model orcomparing measured event data to a model pressure curve ratio. In bothcases, the models include pre-supposed information about the engine, andbuilding those models requires additional time and resources, e.g., fordevelopment and tuning

BRIEF DESCRIPTION OF THE INVENTION

Various embodiments include approaches for determining a top-dead-center(TDC) position of a reciprocating compressor. In various particularembodiments, an apparatus is disclosed. The apparatus can include: apressure transducer configured to measure pressure fluctuations inside acompressor cylinder and convert the pressure fluctuations into anasynchronous waveform; and at least one computing device operablyconnected with the pressure transducer, the at least one computingdevice configured to: extract a data set representing piston angles overa single revolution of a piston within the compressor cylinder from theasynchronous waveform; remove data representing invalid piston anglesfrom the data set to form a refined data set; determine an averagepiston angle for the single revolution from the refined data set; andadjust the refined data set to identify a top-dead-center (TDC) positionof the piston within the compressor cylinder.

A first aspect of the invention includes an apparatus having: a pressuretransducer configured to measure pressure fluctuations inside acompressor cylinder and convert the pressure fluctuations into anasynchronous waveform; and at least one computing device operablyconnected with the pressure transducer, the at least one computingdevice configured to: extract a data set representing piston angles overa single revolution of a piston within the compressor cylinder from theasynchronous waveform; remove data representing invalid piston anglesfrom the data set to form a refined data set; determine an averagepiston angle for the single revolution from the refined data set; andadjust the refined data set to identify a top-dead-center (TDC) positionof the piston within the compressor cylinder

A second aspect of the invention includes a system having: at least onecomputing device configured to identify a top-dead-center (TDC) positionof a piston within a compressor cylinder by performing actionsincluding: obtaining an asynchronous waveform indicating pressurefluctuations inside a compressor cylinder; extracting a data setrepresenting piston angles over a single revolution of the piston withinthe compressor cylinder from the asynchronous waveform; removing datarepresenting invalid piston angles from the data set to form a refineddata set; determining an average piston angle for the single revolutionfrom the refined data set; and adjusting the refined data set toidentify the top-dead-center (TDC) position of the piston within thecompressor cylinder.

A third aspect of the invention includes a computer program producthaving program code, which when executed on at least one at least onecomputing device, causes the at least one computing device to identify atop-dead-center (TDC) position of a piston within a compressor cylinderby performing actions including: obtaining an asynchronous waveformindicating pressure fluctuations inside a compressor cylinder;extracting a data set representing piston angles over a singlerevolution of a piston within the compressor cylinder from theasynchronous waveform; removing data representing invalid piston anglesfrom the data set to form a refined data set; determining an averagepiston angle for the single revolution from the refined data set; andadjusting the refined data set to identify a top-dead-center (TDC)position of the piston within the compressor cylinder.

A fourth aspect of the invention includes a computer-implemented methodperformed using at least one computing device, the computer-implementedmethod including: obtaining an asynchronous waveform indicating pressurefluctuations inside a compressor cylinder; extracting a data setrepresenting piston angles over a single revolution of a piston withinthe compressor cylinder from the asynchronous waveform; removing datarepresenting invalid piston angles from the data set to form a refineddata set; determining an average piston angle for the single revolutionfrom the refined data set; and adjusting the refined data set toidentify a top-dead-center (TDC) position of the piston within thecompressor cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings that depict various embodiments of the invention, in which:

FIG. 1 shows a schematic depiction of an environment, including anapparatus, according to various embodiments of the invention.

FIG. 2 is a flow diagram depicting a process according to variousembodiments of the invention.

FIG. 3 is a flow diagram depicting a sub-process from FIG. 2, accordingto various embodiments of the invention.

FIG. 4 is a flow diagram depicting a sub-process from FIG. 2, accordingto various embodiments of the invention.

FIG. 5 is a flow diagram depicting a sub-process from FIG. 2, accordingto various embodiments of the invention.

FIG. 6 is a flow diagram depicting a sub-process from FIG. 2, accordingto various embodiments of the invention.

It is noted that the drawings of the invention are not necessarily toscale. The drawings are intended to depict only typical aspects of theinvention, and therefore should not be considered as limiting the scopeof the invention. In the drawings, like numbering represents likeelements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

As noted, the subject matter disclosed herein relates to compressorsystems. More particularly, the subject matter relates to diagnostics ofcompressor systems.

As described herein, conventional diagnostic approaches for determiningthe top-dead-center (TDC) position on a reciprocating compressor requirethat the compressor be powered off (shutdown). With the compressor shutdown, a dial indicator or level may be used to determine the TDCposition. With the TDC established, a proximity probe may be installedto view an event on the crankshaft or crosshead. The structure(s) viewedby the proximity probe may be detectable on a once-per-turn ormultiple-event-per-turn basis, or a combination thereof. Afterdetermining the TDC position and installing the proximity probe, thecompressor maybe re-started. The conventional approach relies upon thisproximity probe and an event (referred to as a phase-referencetransducer) along with requisite wiring connecting the probe and thetransducer, to mark TDC for each revolution. Modification of thecompressor and/or crankshaft, installation of wiring, and verificationof components add expense to the diagnostic system.

Additionally, in conventional approaches, the event data must becollected simultaneously across the pressure transducer and thephase-reference transducer so that the TDC marked by the phase-referencetransducer can be accurately related to the pressure transducer. Theneed for this type of simultaneous data collection nearly excludeswireless transmission of data from the compressor as it can be difficultto ensure simultaneous transmission of data from various points,particularly in industrial environments.

As described herein, prior approaches for determining the TDC of areciprocating engine include comparing measured event data to athermodynamic model or comparing measured event data to a model pressurecurve ratio. In both cases, the models include pre-supposed informationabout the engine, and building those models requires additional time andresources, e.g., for development and tuning.

As described herein, the terms “phase-reference transducer” or “PRT” canbe used to refer to a probe which detects a shaft reference point on amoving shaft and provides data about that shaft reference point, e.g.,to a computing device. One commonly used phase-reference transducer isknown commercially as a Keyphasor®, which is a registered trademark ofthe Bently Nevada Corporation, PO Box 157, Minden, Nev. 89423.

Various embodiments of the invention include approaches for determininga TDC of a reciprocating compressor without the use of a phase-referenceelement, which allows for, among other things, wireless sampling andanalysis of data about the reciprocating compressor. Some embodimentsinclude an apparatus having a pressure transducer (also referred to as apressure probe) coupled with at least one computing device. The pressuretransducer can continuously sample asynchronous waveform data about thereciprocating compressor's shaft. As used herein, the term “asynchronouswaveform” or “asynchronous waveform data” is defined as an array ofnumbers, equally spaced in time, that represent pressure fluctuationsinside the cylinder of a compressor (e.g., about the movement of thecompressor shaft within the cylinder). The computing device(s) canextract a single revolution of data from that asynchronous waveformdata, manipulate that extracted data, and determine a portion of thewaveform data that corresponds with the TDC position of the compressor.Various embodiments of the invention are described with reference tomanipulating asynchronous waveform data that represents piston angles ofthe compressor's piston. As used herein, the term “piston angle” refersto the number of degrees of crank rotation from the first sample in thewaveform (asynchronous waveform) to the sample taken at TDC.

Additional embodiments of the invention include a computer programproduct having program code, which when executed on at least one atleast one computing device, causes the at least one computing device toidentify a top-dead-center (TDC) position of a piston within acompressor cylinder by performing actions including: obtaining anasynchronous waveform indicating pressure fluctuations inside acompressor cylinder; extracting a data set representing piston anglesover a single revolution of a piston within the compressor cylinder fromthe asynchronous waveform; removing data representing invalid pistonangles from the data set to form a refined data set; determining anaverage piston angle for the single revolution from the refined dataset; and adjusting the refined data set to identify the top-dead-center(TDC) position of the piston within the compressor cylinder.

Other embodiments of the invention include a computer-implemented methodthat includes performing processes using at least one computing device.The processes can include: obtaining an asynchronous waveform indicatingpressure fluctuations inside a compressor cylinder; extracting a dataset representing piston angles over a single revolution of a pistonwithin the compressor cylinder from the asynchronous waveform; removingdata representing invalid piston angles from the data set to form arefined data set; determining an average piston angle for the singlerevolution from the refined data set; and adjusting the refined data setto identify a top-dead-center (TDC) position of the piston within thecompressor cylinder.

Turning to the drawings, FIG. 1 shows an illustrative environment 10including an apparatus 12 and a (reciprocal motion) compressor 14according to various embodiments of the invention. Environment 10further includes at least one computing device (computer system 20),which includes a top-dead-center (TDC) identification program 30, whichmakes computer system 20 operable to determine a TDC of one or morepistons within the compressor by performing a process described herein.

A portion of the compressor 14 is shown in a cut-away view to illustrateone compressor cylinder 15 housing a piston 16. Also shown, along asidewall of the cylinder 15, is a pressure transducer 17, which can bemounted in a conventional manner along the cylinder 15. The pressuretransducer 17 can include any conventional pressure transducer, e.g., apiezoelectric pressure transducer, capacitive pressure transducer,optical pressure transducer, resonant pressure transducer, thermalpressure transducer, etc.

The pressure transducer 17 can be operably connected (or, “coupled”)with the computer system 20, e.g., via wireless and/or hard-wired means(connection shown via dashed line). In various particular embodiments,the pressure transducer 17 and the computer system 20 are connected viaa hard-wired connection, at least until the computer system 20 extractsat least one revolution of data to determine a TDC position of thepiston 16 (described further herein). In other particular embodiments,the pressure transducer 17 includes at least one component of thecomputer system 20, such that one or more processes performed by thecomputer system 20 can be performed at the pressure transducer 17 (or inthe computer system 20 physically coupled to the transducer 17). FIG. 1shows this embodiment in phantom, where at least one component of thecomputer system 20 is contained within the pressure transducer 17.Various embodiments of the invention are directed toward the apparatus12, which includes the computer system 20 coupled with the pressuretransducer 17. Various other embodiments are directed toward thecomputer system 20, which can obtain data, e.g., from the pressuretransducer 17, and perform processes using that data to determine atop-dead-center (TDC) position of the piston 16 within the compressorcylinder 15. Various other embodiments include methods and computerprogram products which can include functions performed by a computingdevice, e.g., computer system 20.

Computer system 20 is shown including a processing component 22 (e.g.,one or more processors), a storage component 24 (e.g., a storagehierarchy), an input/output (I/O) component 26 (e.g., one or more I/Ointerfaces and/or devices), and a communications pathway 28. In general,processing component 22 executes program code, such as TDCidentification program 30, which is at least partially fixed in storagecomponent 24. While executing program code, processing component 22 canprocess data, which can result in reading and/or writing transformeddata from/to storage component 24 and/or I/O component 26 for furtherprocessing. Pathway 28 provides a communications link between each ofthe components in computer system 20. I/O component 26 can comprise oneor more human I/O devices, which enable a human user 13 to interact withcomputer system 20 and/or one or more communications devices to enable asystem user 13 to communicate with computer system 20 using any type ofcommunications link. To this extent, TDC identification program 30 canmanage a set of interfaces (e.g., graphical user interface(s),application program interface, and/or the like) that enable human and/orsystem users 13 to interact with TDC identification program 30. Further,TDC identification program 30 can manage (e.g., store, retrieve, create,manipulate, organize, present, etc.) the data, such as transducer data40, using any solution. As described herein, transducer data 40 caninclude data gathered and/or transformed by a pressure transducer (e.g.,transducer 17). In some cases, that transducer data 40 can indicatepressure fluctuations inside a compressor cylinder (e.g., cylinder 15),and in some cases, the transducer data 40 can include an asynchronouswaveform transformation of pressure fluctuation data. The asynchronouswaveform can include a series of uniformly spaced data points, whichindicate pressure fluctuation data obtained continuously from thecylinder 15.

In any event, computer system 20 can comprise one or more generalpurpose computing articles of manufacture (e.g., computing devices)capable of executing program code, such as TDC identification program30, installed thereon. As used herein, it is understood that “programcode” means any collection of instructions, in any language, code ornotation, that cause a computing device having an information processingcapability to perform a particular action either directly or after anycombination of the following: (a) conversion to another language, codeor notation; (b) reproduction in a different material form; and/or (c)decompression. To this extent, TDC identification program 30 can beembodied as any combination of system software and/or applicationsoftware.

Further TDC identification program 30 can be implemented using a set ofmodules 32. In this case, a module 32 can enable computer system 20 toperform a set of tasks used by TDC identification program 30, and can beseparately developed and/or implemented apart from other portions of TDCidentification program 30. As used herein, the term “component” meansany configuration of hardware, with or without software, whichimplements the functionality described in conjunction therewith usingany solution, while the term “module” means program code that enables acomputer system 20 to implement the actions described in conjunctiontherewith using any solution. When fixed in a storage component 24 of acomputer system 20 that includes a processing component 22, a module isa substantial portion of a component that implements the actions.Regardless, it is understood that two or more components, modules,and/or systems may share some/all of their respective hardware and/orsoftware. Further, it is understood that some of the functionalitydiscussed herein may not be implemented or additional functionality maybe included as part of computer system 20.

When computer system 20 comprises multiple computing devices, eachcomputing device can have only a portion of TDC identification program30 fixed thereon (e.g., one or more modules 32). However, it isunderstood that computer system 20 and TDC identification program 30 areonly representative of various possible equivalent computer systems thatmay perform a process described herein. To this extent, in otherembodiments, the functionality provided by computer system 20 and TDCidentification program 30 can be at least partially implemented by oneor more computing devices that include any combination of general and/orspecific purpose hardware with or without program code. In eachembodiment, the hardware and program code, if included, can be createdusing standard engineering and programming techniques, respectively.

Regardless, when computer system 20 includes multiple computing devices,the computing devices can communicate over any type of communicationslink. Further, while performing a process described herein, computersystem 20 can communicate with one or more other computer systems usingany type of communications link. In either case, the communications linkcan comprise any combination of various types of optical fiber, wired,and/or wireless links; comprise any combination of one or more types ofnetworks; and/or utilize any combination of various types oftransmission techniques and protocols.

FIG. 2 illustrates a flow chart depicting general processes which can beperformed according to various embodiments of the invention. In somecases, these processes are described with reference to the environment10 of FIG. 1, however, it is understood that various processes can beperformed in accordance with other environments and components notspecifically depicted. These processes can be performed in the ordershown, or in any other order to perform the functions of the inventiondescribed herein. Certain processes are illustrated as not necessarilybeing included in all embodiments by dashed lines. For example,preliminary processes P1 and P2 can be performed according to variousembodiments described herein (e.g., those embodiments employing apressure transducer 17 to gather pressure fluctuation data and convertthat data to an asynchronous waveform). However, in various embodiments,an asynchronous waveforms is obtained, e.g., by at least one computingdevice, without requiring the measurement and conversion processes inP1-P2. As shown, various methods can include:

Process P1: Measuring pressure fluctuations inside a compressor cylinder(e.g., pressure cylinder 15). In various embodiments, the pressuretransducer is configured to measure pressure fluctuations within thecompressor cylinder using conventional methods, e.g., piezoelectric,optical, etc.

Process P2: After measuring pressure fluctuations within the pressurecylinder 15, the pressure transducer 17 can convert that fluctuationdata into an asynchronous waveform, e.g., a continuous data set havingevenly spaced data points representing pressure within the cylinder 15over time. As described herein, the asynchronous waveform can beanalyzed by other elements of the apparatus 12, e.g., the computersystem 20, for the purposes of identifying a top-dead-center (TDC)position of the piston 16 within the cylinder 15. In variousembodiments, the pressure transducer 17 can transmit the asynchronouswaveform data (and in some cases, the raw pressure data) to the computersystem 20 as transducer data 40. It is understood that in alternativeembodiments, the pressure transducer 17 could store the transducer data40 (asynchronous waveform data), e.g., in an internal data store,external data store, or other location for later access by the computersystem 20.

Process P3: At the computer system 20, the TDC identification program 30can obtain the transducer data 40 (including asynchronous waveform data,and in some cases, the raw pressure data), which was previously obtainedby the pressure transducer 17. As noted herein, in some cases, the TDCidentification program 30 can obtain the transducer data 40 from a datastore, or directly from the pressure transducer 17 (via wireless and/orhard-wired means). The TDC identification program 30 can then extract adata set representing piston angles (angles of piston 16 within cylinder15) over a single revolution of the piston 16 within the compressorcylinder 15 from the transducer data 40 (asynchronous waveform data).The process of extracting this single revolution of data is furtherdescribed with reference to the flow diagram of FIG. 3.

Process P4: After extracting the data set representing a singlerevolution of the piston 16 within cylinder 15, the TDC identificationprogram 30 can remove data representing invalid piston angles from thedata set to form a refined data set. Removing invalid piston angle datacan be performed according to various approaches, which may be combinedor used separately to remove data that may inhibit analysis of theasynchronous waveform. Three approaches are shown and described indetail according to various embodiments of the invention. These threeapproaches are described with greater detail referring to FIGS. 4, 5 and6, respectively. The approaches include:

A) Identifying and excluding piston angles based upon a compressionratio of the single revolution of the piston 16 within the compressorcylinder 15 (FIG. 4);

B) Identifying and excluding piston angles based upon a volumetricefficiency of the single revolution of the piston within the compressorcylinder (FIG. 5); and/or

C) Identifying and excluding piston angles based upon a clearance volumeof the single revolution of the piston within the compressor cylinder(FIG. 6).

Process P5: After removing data representing invalid piston angles toform the refined data set, the TDC identification program 30 can takethe refined data set and determine an average piston angle over thesingle revolution, e.g., via conventional averaging techniques known inthe art.

Process P6: After averaging the refined data set, the TDC identificationprogram 30 adjusts the refined data set to identify a top-dead-center(TDC) position of the piston 16 within the compressor cylinder 15. Invarious embodiments, this includes shifting the refined data set by theaveraged value so that the TDC value is the first value in the refineddata set. This process can include graphically displacing the refineddata set along the time domain such that the first value in the refineddata set matches the determined TDC value.

FIG. 3 depicts an example flow diagram including processes in extractinga single revolution of data from the asynchronous waveform according tosome embodiments, as described with reference to Process P3 in FIG. 2.As shown, this process can include:

Process P300: Collect asynchronous data and store that data in an array(also referred to as a waveform).

Process P301: Calculate the average of the waveform data, e.g., viaconventional averaging techniques.

Process P302: Calculate the hysteresis of the waveform data, e.g., usinga default value such as 5% of the average (average determined in ProcessP301).

Process P303: Set a trigger to inactive, and set crossings equal to zero(0).

Process P304: Set a waveform index to the first value in the array, withthe index equal to zero (0).

Decision D305: Is the waveform index less than the hysteresis value? IfYes, set trigger to active and proceed to Decision D306; if No, proceeddirectly to Decision D306.

Decision D306: Is the waveform index greater than the average of thewaveform data AND is the trigger active?

If Yes, proceed to Decision D307.

Decision D307: Is the number of crossings equal to zero (0)?

If No, proceed to Decision D308.

Decision D308: Is the number of crossings equal to one (1)?

If Yes, in Process P309, set indexStop equal to the index, and inProcess P310, set the index equal to waveform length.

Returning to Decision D307, if the number of crossings is equal to zero(0)

(Yes), process P311 includes setting indexStart equal to the index.

Process P312 includes increasing the crossing values (crossings++), andsetting the trigger to inactive.

Returning to Decision D308, if the number of crossings is not equal toone (1) (No), the process flows to Process P312. Similarly, followingprocess P310 (index=waveform length), the method proceeds to ProcessP312.

Returning to Decision D306, if No, Process P313 includes: increase theindex (index++). This Process P313 also follows Process P312.

After process P313; proceed to Decision D314: Is the index greater thanthe waveform length?

If No, return to Decision D305.

If Yes, proceed to Decision D315: Is the number of crossings less thantwo (2)?

If Yes, End.

If No, proceed to Process P316: Remove all points from the waveformoutside of indexStart and indexStop. The graphical depiction adjacentProcess P316 in FIG. 3 illustrates a snapshot of a single revolution ofdata about a piston within a compressor cylinder.

It is understood that the process flows of FIGS. 3-6 can be performedsuccessively, simultaneously, or completely independently according tovarious embodiments of the invention. Linkage between these processflows (as illustrated by connecting nodes (1), (2) (3)) is shown merelyfor illustrative purposes.

FIG. 4 depicts an example flow diagram including processes inidentifying and excluding piston angles based upon a compression ratioof the single revolution of the piston 16 within the compressor cylinder15, according to some embodiments, as described with reference toProcess 4 in FIG. 2. As shown, this process can include:

Process P400: Set variable SampleOffset to the first value in the array(waveform). Process P400 is illustrated with a graphical depictionshowing samples per revolution, where the color white indicates apossibly valid piston angle, and black indicates an invalid pistonangle.

Process P401: Set Valid TDC Index (Sample Offset) array elements totrue.

Process P402: Calculate index values for top-dead-center (TDC) andbottom-dead-center (BDC); set indexTDC=SampleOffset; setindexBDC=(SampleOffset+SamplesPerRev/2)×MOD SamplesPerRev.

Decision D403: Is this data describing the head end of the compressorcylinder?

If No, Process P404: set Compression Ratio=Waveform (index BDC)/Waveform(index TDC);

If Yes, Process P405: set Compression Ratio=Waveform (indexTDC)/Waveform(indexBDC).

In either Yes or No to Decision D403, the process proceeds to DecisionD406: Is the Compression ratio greater than a default value (e.g., 1.5in some cases)?

If No, in process P407: set ValidTDCIndex (Sample Offset) array elementto false.

If Yes, in process P408, increase the SampleOffSet (SampleOffSet++).

Decision D409: Is the SampleOffset greater than the waveform length?

If No, return to Process P401;

If Yes, in some embodiments, the process can proceed to identifying andexcluding piston angles based upon a volumetric efficiency of the singlerevolution of the piston within the compressor cylinder (FIG. 5). Asshown adjacent node (2), a portion of the sample data indicated in blackwas found invalid according to the processes illustrated in FIG. 4.

FIG. 5 depicts an example flow diagram including processes inidentifying and excluding piston angles based upon a volumetricefficiency of the single revolution of the piston 16 within thecompressor cylinder 15, according to some embodiments, as described withreference to Process 4 in FIG. 2. As shown, this process can include:

Process P500: Calculating a volumetric efficiency (VE) for all possiblepiston angles.

Process P501, set variable SampleOffset to the first value in the array(waveform). The first value is usually zero (0).

Decision D502: Is ValidTDCIndex (SampleOffset) false?

If Yes, proceed to Process P509: increase sample offset(SampleOffset++);

If No, proceed to Decision D503: Is suction VE greater than a threshold(e.g., 0.20)?

If No, proceed to Process P504: Set ValidTDCIndex (SampleOffset) arrayelement to false;

If Yes (and if No, after Process P504), proceed to Decision D505: Isdischarge VE greater than a threshold (e.g., 0.10)?

If No, proceed to Process P506: Set ValidTDCIndex (SampleOffset) arrayelement to false.

If Yes (and if No, after Process P506), proceed to Decision D507: Issuction VE greater than discharge VE?

If No, proceed to Process P508: Set ValidTDCIndex (SampleOffset) arrayelement to false.

If Yes (and if No, after Process P508), proceed to Process P509:increase sample offset (SampleOffset++).

Following Process P509, decision D510 includes: Is SampleOffset greaterthan waveform length?

If No, return to Decision D502;

If Yes, in some embodiments, the process can proceed to identifying andexcluding piston angles based upon a clearance volume of the singlerevolution of the piston within the compressor cylinder (FIG. 6). Asshown adjacent node (3), a portion of the sample data indicated in blackwas found invalid according to the processes illustrated in FIG. 5.

FIG. 6 depicts an example flow diagram including processes inidentifying and excluding piston angles based upon a clearance volume ofthe single revolution of the piston 16 within the compressor cylinder15, according to some embodiments, as described with reference toProcess 4 in FIG. 2. As shown, this process can include:

Process P600: Calculate clearance volumes (CV), for all possible pistonangles.

Process P601: Set variable SampleOffset to the first value in the array(waveform), which is typically a value of zero (0). Process P601 isillustrated with a graphical depiction showing samples per revolution,where the color white indicates a possibly valid piston angle, and blackindicates an invalid piston angle.

Decision D602: Is ValidTDCIndex (SampleOffset) false?

If Yes, proceed to Process P609: Increase sample offset(SampleOffset++);

If No, proceed to Decision D603: Is the suction CV less than zero (0)?

If Yes, proceed to Process P604: set ValidTDCIndex (SampleOffset) arrayelement to false;

If No (and if Yes, after Process P604), proceed to Decision D605: Is thedischarge CV less than zero (0)?

If Yes, proceed to Process P606: Set ValidTDCIndex (SampleOffset) arrayelement to false);

If No (and if Yes, after Process P607), proceed to Decision D608: Is(Suction CV/Discharge CV) between a threshold range (e.g., 0.95 and1.05)?

If No, proceed to Process P608: Set ValidTDCIndex (SampleOffset) arrayelement to false;

If Yes (and if No, after process P608), proceed to Process P609:Increase sample offset (SampleOffset++).

Following Process P609, Decision D610 asks: Is the SampleOffset greaterthan the waveform length?

If No, return to Decision D602;

As shown adjacent Decision D610, a portion of the sample data indicatedin black was found invalid according to the processes illustrated inFIG. 6.

If Yes, Proceed to Process P611: Average the remaining possible pistonangles (not indicated as invalid), and that average is used as the indexof the TDC, SampleOffset.

Finally, Process P612: Re-index (adjust) the waveform array so that theTDC is the first element in the waveform.

It is understood that the various processes described herein, e.g.,according to FIGS. 2-6, may be performed using the computer system 20,including the TDC identification program 30 (FIG. 1). The computersystem 20 can obtain and manipulate transducer data 40 according to anyof the embodiments described herein.

In any event, computer system 20 can obtain transducer data 40 using anysolution. For example, computer system 20 can generate and/or be used togenerate transducer data 40, retrieve transducer data 40 from one ormore data stores, receive transducer data 40 from another system, and/orthe like.

While shown and described herein as a method and system for providing aTDC identification program, it is understood that aspects of theinvention further provide various alternative embodiments. For example,in one embodiment, the invention provides a computer program fixed in atleast one computer-readable medium, which when executed, enables acomputer system to determine a top-dead-center location in areciprocating compressor. To this extent, the computer-readable mediumincludes program code, such as TDC identification program 30 (FIG. 1),which enables a computer system to implement some or all of a processdescribed herein. It is understood that the term “computer-readablemedium” comprises one or more of any type of tangible medium ofexpression, now known or later developed, from which a copy of theprogram code can be perceived, reproduced, or otherwise communicated bya computing device. For example, the computer-readable medium cancomprise: one or more portable storage articles of manufacture; one ormore memory/storage components of a computing device; paper; and/or thelike.

In another embodiment, the invention provides a method of providing acopy of program code, such as TDC identification program 30 (FIG. 1),which enables a computer system to implement some or all of a processdescribed herein. In this case, a computer system can process a copy ofthe program code to generate and transmit, for reception at a second,distinct location, a set of data signals that has one or more of itscharacteristics set and/or changed in such a manner as to encode a copyof the program code in the set of data signals. Similarly, an embodimentof the invention provides a method of acquiring a copy of the programcode, which includes a computer system receiving the set of data signalsdescribed herein, and translating the set of data signals into a copy ofthe computer program fixed in at least one computer-readable medium. Ineither case, the set of data signals can be transmitted/received usingany type of communications link.

In still another embodiment, the invention provides a method ofgenerating TDC identification program. In this case, a computer system,such as computer system 20 (FIG. 1), can be obtained (e.g., created,maintained, made available, etc.) and one or more components forperforming a process described herein can be obtained (e.g., created,purchased, used, modified, etc.) and deployed to the computer system. Tothis extent, the deployment can comprise one or more of: (1) installingprogram code on a computing device; (2) adding one or more computingand/or I/O devices to the computer system; (3) incorporating and/ormodifying the computer system to enable it to perform a processdescribed herein; and/or the like.

In any case, the technical effect of the TDC identification program 30shown and described herein is to identify a top-dead-center position ofa piston within a cylinder of a reciprocating compressor.

The foregoing description of various aspects of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and many modifications and variations are possible. Suchmodifications and variations that may be apparent to an individual inthe art are included within the scope of the invention as defined by theaccompanying claims.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

I claim:
 1. An apparatus comprising: a pressure transducer configured tomeasure pressure fluctuations inside a compressor cylinder and convertthe pressure fluctuations into an asynchronous waveform; and at leastone computing device operably connected with the pressure transducer,the at least one computing device configured to: extract a data setrepresenting piston angles over a single revolution of a piston withinthe compressor cylinder from the asynchronous waveform; remove datarepresenting invalid piston angles from the data set to form a refineddata set; determine an average piston angle for the single revolutionfrom the refined data set; and adjust the refined data set to identify atop-dead-center (TDC) position of the piston within the compressorcylinder.
 2. The apparatus of claim 1, wherein the at least onecomputing device is configured to remove the data representing invalidpiston angles from the data set by identifying and excluding pistonangles based upon a compression ratio of the single revolution of thepiston within the compressor cylinder.
 3. The apparatus of claim 1,wherein the at least one computing device is configured to remove thedata representing invalid piston angles from the data set by identifyingand excluding piston angles based upon a volumetric efficiency of thesingle revolution of the piston within the compressor cylinder.
 4. Theapparatus of claim 1, wherein the at least one computing device isconfigured to remove the data representing invalid piston angles fromthe data set by identifying and excluding piston angles based upon aclearance volume of the single revolution of the piston within thecompressor cylinder.
 5. The apparatus of claim 1, wherein the at leastone computing device is configured to adjust the refined data set toposition a data value corresponding to the TDC position of the pistonwithin the compressor as a first data value in the refined data set. 6.The apparatus of claim 1, wherein the asynchronous waveform includes aseries of uniformly spaced time domain data points.
 7. The apparatus ofclaim 1, wherein the at least one computing device is configured toextract the data set representing the piston angles over the singlerevolution using a threshold-hysteresis model.
 8. A system comprising:at least one computing device configured to identify a top-dead-center(TDC) position of a piston within a compressor cylinder by performingactions including: obtaining an asynchronous waveform indicatingpressure fluctuations inside a compressor cylinder; extracting a dataset representing piston angles over a single revolution of the pistonwithin the compressor cylinder from the asynchronous waveform; removingdata representing invalid piston angles from the data set to form arefined data set; determining an average piston angle for the singlerevolution from the refined data set; and adjusting the refined data setto identify the TDC position of the piston within the compressorcylinder.
 9. The system of claim 8, wherein the at least one computingdevice is configured to remove the data representing invalid pistonangles from the data set by identifying and excluding piston anglesbased upon a compression ratio of the single revolution of the pistonwithin the compressor cylinder.
 10. The system of claim 8, wherein theat least one computing device is configured to remove the datarepresenting invalid piston angles from the data set by identifying andexcluding piston angles based upon a volumetric efficiency of the singlerevolution of the piston within the compressor cylinder.
 11. The systemof claim 8, wherein the at least one computing device is configured toremove the data representing invalid piston angles from the data set byidentifying and excluding piston angles based upon a clearance volume ofthe single revolution of the piston within the compressor cylinder. 12.The system of claim 8, wherein the at least one computing device isconfigured to adjust the refined data set to position a data valuecorresponding to the TDC position of the piston within the compressor asa first data value in the refined data set.
 13. The system of claim 8,wherein the asynchronous waveform includes a series of uniformly spacedtime domain data points.
 14. The system of claim 8, wherein the at leastone computing device is configured to extract the data set representingthe piston angles over the single revolution using athreshold-hysteresis model.
 15. A computer program product comprisingprogram code, which when executed on at least one at least one computingdevice, causes the at least one computing device to identify atop-dead-center (TDC) position of a piston within a compressor cylinderby performing actions including: obtaining an asynchronous waveformindicating pressure fluctuations inside the compressor cylinder;extracting a data set representing piston angles over a singlerevolution of a piston within the compressor cylinder from theasynchronous waveform; removing data representing invalid piston anglesfrom the data set to form a refined data set; determining an averagepiston angle for the single revolution from the refined data set; andadjusting the refined data set to identify the top-dead-center (TDC)position of the piston within the compressor cylinder.
 16. The computerprogram product of claim 15, wherein the removing of the datarepresenting invalid piston angles from the data set includesidentifying and excluding piston angles based upon a compression ratioof the single revolution of the piston within the compressor cylinder.17. The computer program product of claim 15, wherein the removing ofthe data representing invalid piston angles from the data set includesidentifying and excluding piston angles based upon a volumetricefficiency of the single revolution of the piston within the compressorcylinder.
 18. The computer program product of claim 15, wherein theremoving of the data representing invalid piston angles from the dataset includes identifying and excluding piston angles based upon aclearance volume of the single revolution of the piston within thecompressor cylinder.
 19. The computer program product of claim 15,further comprising: adjusting the refined data set to position a datavalue corresponding to the TDC position of the piston within thecompressor as a first data value in the refined data set.
 20. Thecomputer program product of claim 15, wherein the asynchronous waveformincludes a series of uniformly spaced data points, and wherein theextracting of the data set representing the piston angles over thesingle revolution includes using a threshold-hysteresis model.